I worked with a legal migrant who filled a serious skills shortage by his presence. He was told that any dip in his bank balance, any infringement of the law and he was gone. He had to wait 5 years and pay quite a lot of money out to earn his right to stay. He was scared to drive in case he inadvertently got caught for parking or speeding. So why is this not applied to the illegals too?
Some judges will add a deportation order to sentences, but many do not, and appeal seems easy on the grounds of having made a life here. Even those who have these can walk free out of court/prison and disappear, as do those who have been refuse asylum, because there is a disconnect with the police.
There is great difficulty in getting any background on refugees, especially given that their regimes would declare them criminals. The ongoing issues in Somalia/Somaliland bring people in. A discussion with a Somali, many of whom have French as a second language, was why they risked the crossing. His reply was about our "kindness" being legend across his homeland. He worked at a centre supporting new arrivals with language lessons, signposting to housing and services, access to computers and some basic education. This was closed down due to council cuts.
There IS support for mentally ill people, and it is considered a valid reason for not sending them home. I guess though, it is a good or bad as it is for the rest of us.